Parasites residing in the biliary tree include Clonorchis sinensis, Opisthorchis viverrini, Opisthorchis felineus, and Fasciola hepatica. They are willowy, leaf-like, flat flukes dwelling in the bile ducts and gallbladder. Human ascarides, Ascaris lumbricoides, dwelling in the small intestine, inadvertently migrate into the bile ducts and cause biliary obstruction. The purpose of this article is to illustrate typical imaging findings of liver fluke infection and biliary ascariasis.Adult flukes of Clonorchis and Opisthorchis measure 8-15 mm and adult flukes of Fasciola measure 20-40 mm in length. The presence of flukes in the bile ducts causes dilatation of the bile ducts, varying degrees of chronic inflammation followed by adenomatous hyperplasia, and bile duct wall thickening. Imaging findings of clonorchiasis and opisthorchiasis include visualization of adult flukes in the bile ducts and gallbladder, diffuse dilatation of the peripheral small intrahepatic bile ducts with no or minimal dilatation of the large bile ducts, and thickening of the bile duct wall. In biliary fascioliasis and ascariasis, adult worms are visualized in the dilated bile ducts and gallbladder.